UWB (Ultra Wide Band) technology is capable of transmitting data at a high data transmission rate within a limited range.
The channel capacity is dependent on the available channel bandwidth. In line with Shannon's equation, the channel capacity is calculated as: C=BWLOG 2(1+SNR) where C is the channel capacity in bits per second, BW is the available channel bandwidth in Hz, and SNR is the signal-to-noise ratio.
Ultra-wideband (UWB) technology provides a very high level of frequency bandwidth. First-generation UWB systems provide a frequency bandwidth of between 3.1 and 5 GHz, and UWB systems from subsequent generations provide a frequency bandwidth of between 3.1 and 10.6 or between 3.1 and 8 GHz. The high level of available channel bandwidth means that the transmission capacity is very high. The low signal transmission powers means that the range of UWB transmitters is relatively short and is no more than 10 meters.
FIG. 1 shows a UWB arrangement based on the prior art. A transmitter uses a transmission antenna to send a UWB signal to a reception antenna on a receiver. The UWB receiver contains a bandpass filter BPF which allows signals to pass in the admissible spectrum of the UWB system, for example in a frequency range between 3.1 and 10.6 GHz. The UWB received signal is then amplified by a wideband amplifier with little noise output. The wideband LNA (Low Noise Amplifier) has its output connected to the signal processing circuit in the receiver.
FIG. 2 shows a wideband LNA based on the prior art, as is described in R. Gilmore and L. Besser “Practical RF Circuit Design for modern Wireless Systems”, volume II Active Circuits and Systems ISBN 1-58053-522-4. The wideband signal amplifier for amplifying the UWB received signal based on the prior art is designed such that it amplifies the entire UWB signal spectrum in a frequency range between 3.1 and 10.6 GHz, for example. The very high frequency range which needs to be amplified uniformly by the wideband amplifier means that the circuit complexity for such a wideband LNA based on the prior art is very high. In addition, the wideband LNA based on the prior art has the drawback that it has a very high power consumption.
In the case of ultra-wideband systems based on the prior art, there are two fundamentally different embodiments. In DSS (Direct Spread Spectrum) UWB systems, the entire wideband frequency spectrum is used for transmitting the UWB signal. In a multiband UWB system, the wideband frequency spectrum, which ranges from 3.1 to 10.6 GHz, for example, is divided into frequency bands which have a minimum bandwidth of 500 MHz. In the case of this multiband UWB, the transmitter transmits the UWB transmission signal in different frequency bands or channels in line with a prescribed frequency hopping scheme, which is also known to the associated receiver. If the entire UWB frequency band, which ranges from 3.1 to 10.6 GHz, is divided into 15 frequency bands, for example, i.e. 15 different transmission channels, the transmitter hops to and fro between the various channels K.sub.i during transmission in line with a prescribed signal hopping scheme. By way of example, the transmitter hops to the channel K.sub.2, then to channel K.sub.3, then to channel K.sub.7 and finally back to channel K.sub.2. The channel hopping scheme in question is then K.sub.2, K.sub.3, K.sub.7.
In this case, the transmission channel hopping scheme may comprise all or just some of the possible transmission channels.
To date, multiband UWB receivers based on the prior art have also used wideband signal amplifiers which have the aforementioned drawbacks, such as high circuit complexity and high power consumption.
It is therefore the object of the present invention to provide a signal amplifier for a UWB receiver which is simple to implement in terms of circuitry and has a low power consumption.
The invention achieves this object by means of an amplifier having the features cited in patent claim 1.
The invention provides an amplifier for an ultra-wideband (UWB) signal receiver having a signal input for receiving an ultra-wideband signal which is sent by a transmitter and which is transmitted in a sequence of transmission channels (which each have a particular frequency bandwidth) which has been agreed between the transmitter and the receiver, a transistor whose control connection is connected to the signal input, a resonant circuit which is connected to the transistor and whose resonant frequency can be set for the purpose of selecting the transmission channel in line with the agreed sequence of transmission channels, and having a signal output for outputting the amplified ultra-wideband signal, the signal output being tapped off between the transistor and the resonant circuit.
In one preferred embodiment of the inventive amplifier, the resonant circuit has a coil and a plurality of capacitors which are connected in parallel.
In this case, each capacitor is preferably connected to a controllable switch.
The switches are preferably switched on the basis of a control signal which is output by a control device.
In one preferred embodiment of the inventive amplifier, a cascode stage is provided between the transistor and the signal output.
In a first embodiment of the inventive amplifier, the transistors are MOS field-effect transistors.
In an alternative embodiment of the inventive amplifier, transistors are bipolar transistors.
In one preferred embodiment of the inventive amplifier, the frequency bandwidth of a transmission channel is approximately 500 MHz.
The transmission channel sequence is preferably agreed between the transmitter and the receiver in an initialization mode.
In one preferred embodiment, a memory device is provided which is used for storing the agreed transmission channel sequence.
In one preferred embodiment, the receiver has a controller which applies signal control words to an internal decoding circuit in the amplifier in line with the stored transmission channel sequence.
The decoding circuit preferably actuates the controllable switches to change the resonant frequency of the resonant circuit.
In one preferred embodiment, a matching circuit for matching the input impedance of the amplifier to the impedance of a reception antenna on the receiver is provided at the signal input of the amplifier.
In one preferred embodiment, the impedance matching is performed by the matching circuit on the basis of the channel control words which are applied by the controller.
In one particularly preferred embodiment of the inventive amplifier, the amplifier is of fully differential design.
The text below describes preferred embodiments of the inventive amplifier with reference to the appended figures in order to explain features which are fundamental to the invention.